Clinical thermometers are very helpful in the diagnosis of diseases. The tympanic membrane is generally considered by the medical community to be superior to oral, rectal, or underarm sites for representing the body's core temperature. The temperature of the tympanic membrane can be measured by detecting the infrared radiation from the tympanic membrane in the ear canal. In addition, the time needed for the body temperature measuring by using an infrared thermometer is short. The use of infrared thermometers therefore has become more and more prevalent.
To measure the infrared emission in the external car canal, the probe of a tympanic thermometer has to be inserted into the external ear canal for sensing the infrared emission from the tympanic membrane to determine the temperature of the tympanic membrane. However, a tympanic thermometer that is used to determine the body temperature of different patients can cause contamination and infections. To prevent this disadvantage, the probe of a tympanic thermometer can be provided with a probe cover that is disposable after use.
Referring to FIG. 1, a probe cover of a tympanic thermometer disclosed in U.S. Pat. No. 5,163,418 to Fraden et al. comprises a sheath 31 and ring-shaped base 32. The sheath 31 is formed from a infrared transparent film having a thickness of 0.001 inch. The closed end of the sheath 31 is flat and acts as a window 311 for infrared emission. The circumferential wall 312 includes a plurality of pleats. The circumferential peripheral flange is attached to the ring-typed base 32. The base 32 is designed to fit tightly on the probe of the thermometer. When the base 32 is fitted on the probe of the thermometer, the window 311 contacts with the front inlet of the probe. The drawback of the probe cover lies in that when it is inserted in the ear canal, the pleats on the wall 312 of the sheath 31 scrape the skin of the canal and cause a patient feel uncomfortable. In addition, the sheath generates noises when it is pressed. Moreover, wrinkles appear on the window 31 when the probe cover is fitted on the probe and cause stray radiation that adversely affects the accuracy of the measured temperature.
Referring to FIG. 2, a probe cover of a tympanic thermometer disclosed in U.S. Pat. No. 5,088,834 to Howe et al. comprises a frustum-shaped sheath 41 and a base 42 formed from a single piece of infrared transparent material. The dimensions of the sheath 41 are chosen to let it fit on the probe closely. The thickness of the sheath 41 is gradually reduced from the proximal portion to the distal portion such that the window 411 has the minimal thickness of between approximately one thousandth and five then thousandths of an inch. The base 42 circumferentially engages with the open end (proximal end) of the sheath 41 for securing the sheath 41 on the probe of the thermometer. This type of sheath has no pleats and is comfortable for use. However, its disadvantage lies in that the sheath is formed by plastically deforming the material from its proximal open end to its distal closed end. The material is plastically deformed in a significant length so that the maximum thickness change of the material is from 0.03 in. to 0.0005 in. and this causes difficulty in quality control during the manufacturing process.